1. Field of the Invention
The present invention relates generally to molecular biology and biochemistry and more specifically to a subunit of a protein kinase, the IκB kinase, which is activated in response to environmental stresses and proinflammatory signals to phosphorylate inhibitors of NF-κB.
2. Background Information
In chronic inflammatory disease including asthma, rheumatoid arthritis, inflammatory bowel disease and psoriasis, cytokines recruit activated immune and inflammatory cells to the site of lesions, thereby amplifying and perpetuating the inflammatory states. Although the causes of chronic inflammatory disease are in large part unknown, both genetic and environmental factors contribute to pathology. Genes such as those for HLA antigens in rheumatoid arthritis and inflammatory bowel disease can determine a patient's susceptibility to the disease and disease severity, and environmental factors can determine its course. Once established, a chronic inflammatory process is virtually impossible to disrupt; there is no curative treatment for any chronic inflammatory disease. Although chronic disease can be suppressed by glucocorticoid or immunosuppressive therapy, side effects are associated with prolonged treatment.
A ubiquitous transcription factor, nuclear factor-κB (NF-κB), has been identified as of particular importance in immune and inflammatory responses. NF-κB increases the expression of the genes for many cytokines, enzymes, and adhesion molecules in chronic inflammatory diseases. One gene regulated by NF-κB is the gene for inducible nitric oxide synthase, the expression of which is increased in airway epithelial cells and macrophages in patients with asthma; in colonic epithelial cells of patients with the inflammatory bowel disease, ulcerative colitis; and in synovial cells in inflamed joints. The increased expression is reflected by an increased amount of nitric oxide in the exhaled breath of patients with asthma and in the colons of patients with active ulcerative colitis, as well as by elevated urinary nitrite concentrations in patients with rheumatoid arthritis. Cyclooxygenase-2, another inducible enzyme regulated by NF-κB, is responsible for the increased production of prostaglandins and thromboxane in inflammatory diseases.
NF-κB also is involved in expression of adhesion molecules, which recruit inflammatory cells such as neutrophils, eosinophils and T lymphocytes from the circulation to the site of inflammation in all chronic inflammatory diseases. NF-κB regulates the expression of several genes that encode adhesion molecules such as intercellular adhesion molecule 1, vascular cell adhesion molecule 1, and E-selectin.
The production of pro-inflammatory cytokines also can be regulated by NF-κB. Interleukin-1β, TNF-α, interleukin-6, granulocyte-macrophage colony-stimulating factor, and many chemotactic cytokines (chemokines) is increased in patients with asthma, rheumatoid arthritis, psoriasis and inflammatory bowel disease, and all have important roles in the inflammatory process. Interleukin-1β and TNF-α appear to influence severity of disease, possibly by persistent activation of NF-κB.
Thus, the transcription factor NF-κB plays a central role in inflammatory disease. This role is emphasized by the targeted disruption of an inhibitor of NF-κB in mice, which resulted in prolonged activation of NF-κB in response to inflammatory stimuli, and the death of these animals due to widespread inflammation.
Unfortunately, the available therapies for chronic inflammatory diseases such as asthma, rheumatoid arthritis and inflammatory bowel disease are unsatisfactory. Identification of molecules that regulate NF-κB would provide new strategies for screening for anti-inflammatory therapeutics. The present invention satisfies this need by providing the novel IκB kinase subunit, IKK-γ, which is an essential regulatory subunit of the IκB kinase required for NF-κB activation. Related advantages also are provided.